A generator of this type is disclosed in U.S. Pat. No. 5,187,934. To insert the sleeve seals into the housing, it was previously customary to close the cylinders by a cover on their end disposed in the actuating direction, while a ring seal was screwed or wedged at the opposite end (on the driver's side) having the purpose of guiding the push rod that points to the driver as well as serving as an abutment for the secondary piston. Although the inside surface of the cylinder does not require special machining, the prior art master cylinders with plunger pistons suffer from a number of disadvantages. The diameter of the master cylinder is of a considerable size because a plurality of parts must be inserted in each other in an axial direction. Further, there is need for a large number of components to provide for the necessary abutment surfaces for the sealing sleeves.
Efforts directed to economizing the closing cap that is positioned in the actuating direction in the mentioned master cylinders become apparent from patent literature (e.g. from EP 1018459, DE-OS 3905917). As a consequence, housings have been step-like expanded towards the driver in order to arrange for the necessary abutment surfaces for the seal.
Partly, no primary sleeves have been inserted in master cylinders of this type. Resiliently preloaded valve members substituted them instead.